Biodiversity Patterns of Early–Middle Ordovician Marine Microphytoplankton in South China

Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 318–334 Contents lists available at ScienceDirect Palaeogeography, Palaeoclimatology, Palaeoecology journal homepage: www.elsevier.com/locate/palaeo Biodiversity patterns of Early–Middle Ordovician marine microphytoplankton in South China Kui Yan a,b,c,⁎, Thomas Servais c, Jun Li a,b, Rongchang Wu a, Peng Tang a,b a Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39, East Beijing Road, 210008 Nanjing, China b State Key Laboratory of Palaeobiology and Stratigraphy, Nanjing 210008, China c FRE 3298 du CNRS, Géosystèmes, Université de Lille1, SN5, USTL, F-59655 Villeneuve d'Ascq, France article info abstract Article history: Based on new materials from six sections and all available literature data, new diversity curves are presented Received 22 June 2010 for the phytoplankton (acritarchs) from South China, covering the Early–Middle Ordovician interval, when Received in revised form 18 October 2010 the Great Ordovician Biodiversification Event took place. The total diversity curve and the origination data Accepted 9 November 2010 imply that a major radiation of the phytoplankton occurred during the analysed interval. A peak of the total Available online 13 November 2010 acritarch diversity curve appears in the A. suecicus graptolite biozone. The diversity changes vary in the different parts of the investigated area, most probably depending on the position of the analysed sections on Keywords: the carbonate shelf or the slope, reflecting diversity differences due to the position on an inshore–offshore Acritarchs Early–Middle Ordovician transect. South China The Early–Middle Ordovician diversity pattern of the phytoplankton is compared with those of several marine Biodiversity invertebrate groups. Compared with the diversity curve peak of the acritarchs, the conodonts and brachiopods Sea-level changes reached their highest diversities before the acritarchs, while the highest diversity of the chitinozoans appears slightly later. The graptolites show two peaks during the Early–Middle Ordovician, while the trilobites diversity curve shows a peak only in the Sandbian. The different fossil groups, such as chitinozoans, conodonts, graptolites, brachiopods and trilobites show therefore different evolutionary patterns to that of the acritarchs, that are not yet fully understood, and correlations are so far difficult. The acritarch diversity changes can partly be compared to the local sea-level changes from four sections in South China. At a larger scale, the acritarch radiation coincides with a general transgression. At a regional or local scale, correlations are not straightforward, pointing out that more detailed data, based on both acritarch studies and more precise sea-level investigations, are necessary. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Although more than 40 papers were focused on the Ordovician acritarchs in South China, the Ordovician radiation of acritarchs is far The Great Ordovician Biodiversification Event (GOBE) is one of the from being completely understood. Most paper focused on biostratig- most significant radiations of marine organisms during Earth history, raphy (Li et al., 2002b,c), and a few highlighted the importance of the showing a rapid increase in biodiversity and an important ecological South Chinese palaeogeography for palaeobiogeographical considera- evolution (Harper, 2006; Servais et al., 2008, 2009, 2010). Webby et al. tions of the acritarchs (Li, 1989, 1991; Li and Servais, 2002; Servais et al., (2004a) published a synthesis on the Ordovician radiation which 2003). In the last decade, several papers analysed the biodiversity of the documented the biodiversity curves of approximately 25 fossil groups. South Chinese phytoplankton in the Ordovician. Tongiorgi et al. (2003) In the Proterozoic and Palaeozoic fossil record, most acritarchs are implied that the acritarch diversity changes in the Dawan Formation considered to represent marine phytoplankton cysts which constitute from the Daping section in Yichang may be affected by inshore–offshore the fossil record of one part of the base of the marine food chain. and climatic trends. Servais et al. (2004) reviewed the global Ordovician Servais et al. (2008) related ‘the Ordovician plankton revolution’ to acritarch literature and illustrated an acritarch diversity curve of South the diversification of the phytoplankton as evidenced by the record of China. Li et al. (2004) discussed the inshore–offshore trend of acritarch acritarchs and prasinophytes. distributions and acritarch diversity variations from seven South China localities during the interval of the deflexus–suecicus graptolite biozones. Yan et al. (2005) discussed the implication of the acritarch diversity ⁎ Corresponding author. Nanjing Institute of Geology and Palaeontology, Chinese changes from the Meitan Formation from the Honghuayuan section, Academy of Sciences, 39, East Beijing Road, 210008 Nanjing, China. Tongzi. Li and Yan (2006) reviewed the Ordovician acritarch diversity E-mail addresses: [email protected] (K. Yan), [email protected] (T. Servais), [email protected] (J. Li), [email protected] (R. Wu), changes in South China and pointed out an acritarch biodiversity event [email protected] (P. Tang). in the Early–Middle Ordovician. The publication of Li et al. (2007) 0031-0182/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2010.11.012 K. Yan et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 299 (2011) 318–334 319 focused on the Ordovician acritarch diversity counted from the prepared for diversity analysis herein. Acritarch diversity curves of literature and sea-level change in China. South China analysed from the literature data are also presented. In recent years, marine biodiversity changes from China were investigated in the project on the ‘Origination, Radiation, Extinction 2. Material and methods and Recovery in the Geological History’ (e.g., Rong et al., 2007) concerning several taxonomic groups of Ordovician marine organisms 2.1. New material in South China, such as graptolites (Zhang et al., 2007), brachiopods (Zhan et al., 2005, 2006), and trilobites (Zhou et al., 2007). The In order to understand acritarch diversity patterns in South China, diversity of other fossil groups has also been investigated, such as that 160 samples for palynological and diversity analysis were collected from of chitinozoans (Paris et al., 2004; Wang and Chen, 2004), and six sections, 45 samples from the Meitan Formation, Honghuayuan conodonts (Wang and Wu, 2007; Wu et al., 2010). section in Tongzi (Guizhou); seven samples from the Guanyinqiao Ordovician microphytoplankton biodiversity curves and their impli- section in Qijiang (Chongqing); 14 samples from the Dacao Formation cations have been discussed from several other palaeocontinents. Vecoli and Yingpan Formation, Houping section in Chengkou (Chongqing); 34 and Le Hérissé (2004) provided a detailed Ordovician acritarch diversity samples from the Dawan Formation, Huanghuachang section in Yichang curve from the northern margin of South Gondwana. They inferred that (Hubei); nine samples from the Dawan Formation, Daping section in the acritarch diversity curve is hardly compared to the second order sea- Yichang (Hubei); and 51 samples from the Ningkou Formation, level change, and the acritarch diversity changes would be well Huangnitang section in Changshan (Zhejiang) (Fig. 1). correlated to that of the chitinozoans during the Ordovician. Molyneux During the Early and Middle Ordovician, from northwest to (2009) suggested an acritarch diversity evolutionary pattern based on southeast, the South China tectonic plate comprised the Yangtze investigations from deep-water settings in northern England. Ordovician Platform, the Jiangnan Slope, and the Zhujiang Basin (Chen et al., 1995) acritarch diversity curves from the palaeocontinent Baltica have been and Early–Middle Ordovician rocks were deposited in southwest– studied by Hints et al. (2010). Diversity patterns of Ordovician acritarchs, northeast band-like zones (Zhang et al., 2002). The six sections chitinozoans and scolecodonts show some similarities in Baltica and the investigated here are located in different lithofacies. The Honghuayuan acritarch diversity curve can be related to that of other fossil groups in section in Tongzi, the Guanyinqiao section in Qijiang and the Houping some extent (Hints et al., 2010). section in Chengkou are located in an inner-shelf mud–carbonate belt The objective of the present paper is to analyse the Early–Middle during the latest Early–earliest Middle Ordovician which is character- Ordovician acritarch diversity in South China and its relationship with ised by the dominance of carbonate sediments mixed with argillaceous the diversity of other fossil groups and the sea-level change. The and sandy intercalations (Zhang et al., 2002). The Huanghuachang and acritarch assemblages from six sections in South China have been Daping sections in Yichang are located in a shallower outer-shelf 105˚ 110˚ 115˚ 120˚ SHAANXI JIANGSU HENAN Min 13 4 12 Han River 24 11 ANHUI Jialing Nanjing 14 SICHUAN River Hefei HUBEI River 8 Chengdu 7 6 River 9 Wuhan Yangtze 30˚ 30˚ 5 120˚ 25 CHONGQING Yalong ZHEJIANG Chongqing 1 3 2 17 15 River 18 16 Nanchang 26 19 10 Changsha HUNAN JIANGXI GUIZHOU FUJIAN 20 Fuzhou Guiyang YUNNAN 21 27 22 29 28 23 20˚ 30 GUANGXI 20˚ 0 100 200km Kunming 105 110˚ 115˚ Fig. 1. Locality map of

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